Acquisition (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Acquisition
Total revenues - Pro forma	$ 2,216.6	$ 2,159.1
Net income (loss) - Pro forma	$ 217.6	$ 250.2
Basic earnings (loss) per common share (in dollars per share) - Pro forma	$ 0.74	$ 0.83
Diluted earnings (loss) per common share (in dollars per share) - Pro forma	$ 0.73	$ 0.82